The present invention relates to the mechanical forming of semi-finished metallic products such as plates, bars and other similar elements and, more specifically, it concerns an adjustable forming die, in particular for a forming press.
It is well known that presses for the mechanical forming of metallic elements comprise dies, supported by a bed, which are substantially xe2x80x9cVxe2x80x9d shaped and in turn able to support the element to be formed in opposition to the thrust that is exerted centrally to the element by a forming punch.
To change the distance between the bearing areas of the elements to be formed on the die, the prior art provides for dies in which two independent and movable half-dies can be positioned at a variable distance from each other to provide, in mutual combination, a bearing in which the xe2x80x9cVxe2x80x9d is more or less open depending on requirements.
Currently, the distance of the half-dies is adjusted through a system of mechanized wedges positioned between the half-dies and the bed. The wedges provide not only the capability of adjusting the distance, but also the ability to transmit to the bed the intense mechanical stresses exchanged between punch and die when the press is in use.
The wedges are positioned between parallel, vertical and opposite shoulders of the half-dies and of the bed; they work coupled with each other, reacting against said shoulders; and they are distributed at regular intervals longitudinally to the half-dies.
The angle of inclination of the wedges and of the corresponding counter-wedge of each pair is constructively limited to a few degrees. It is not possible to use wedges having inclinations greater than 7-8xc2x0, because said inclinations would render the mechanism reversible, and hence unusable.
In consideration of the above, to have a range of adjustment of the distance between the half-dies of acceptable amplitude, it is necessary to have rather long wedges available. Correlated to said length is also the minimum distance that, constructively, must separate the various pairs of wedges, that succeed each other longitudinally to the half-die of interest, to prevent mechanical interference during the adjustment of the distance between the half-dies.
As a consequence of the geometric and mechanical aspects described above, known dies are the result of a design compromise able to mediate different and mutually conflicting aspects. Said compromise cannot ignore an additional element represented by the fact that the very operation of a wedge and of a counter-wedge coupled therewith implies a continuous variation of the contact surface between wedge and counter-wedge. If the coupling surface reaches the minimum extension, between wedge and counter-wedge structural limits can be reached, connected with the reaching of excessive contact pressures for the local strength of the material constituting the wedges.
For the reasons set out above, prior art solutions therefore have practically insurmountable technical limits. To reach a pre-defined minimum distance between the half-dies, without having an insufficient contrast surface area between wedge and counter-wedge, it is necessary to build very long wedges. But very long wedges imply equally long intervals between the contiguous pairs of wedges that follow each other along the die; variable and large intervals, that in addition to influencing the longitudinal dimensions of the die, also influence the elastic deformability of the shoulders, implying in the die or in the press that uses it, deformations that in turn influence on one hand the construction of the die and of the press and on the other hand the precision of execution of the forming operation itself.
The aim of the present invention therefore is to overcome the characteristic limits of the forming dies used in known forming presses by means of a different and more advantageous mechanism for adjusting the distance of the half-dies and transmitting stresses between punch and die.
In accordance with the invention, said aim is achieved by a forming die, in particular for a forming press, comprising a pair of half-dies, supported by a bed, able in turn to support an element to be deformed permanently in opposition to the thrust exerted by a forming punch, comprising for at least one of said half-dies, two racks, respectively associated to the half-die and to the bed, provided with at least a pair of oblique teeth, set side by side, which racks are associated in mutual opposition with teeth of the one inserted between the teeth of the other, said teeth being correspondingly coupled on at least two parallel and oblique contact planes, mutually meshing in such a way as to vary the distance between the half-dies in correspondence with the relative translation of the racks effected longitudinally to the half-dies themselves.
The presence of at least two pairs of meshed teeth allows, retaining all other conditions equal with the systems used in prior art applications, to double the extension of the contact surface along which the teeth transmit the forces exchanged between punch and die.
However, if the racks are provided with multiple pairs of teeth, set mutually side by side, as many parallel contact surfaces as desired may be obtained.
This allows to obtain the total contact surface area of the extension best suited for one""s own application, without thereby submitting to any geometric constraint related to the inclination of the teeth and to their longitudinal development.
If one then also causes thexe2x80x94single or multiplexe2x80x94pairs of teeth that follow each other longitudinally to the half-dies to have their teeth extended in such a way that their longitudinal projections are superposed, the reaction consequent to the loads exchanged between the teeth that is discharged on the shoulders of the bed or of the half-dies can be uniformly distributed over the length in such a way as to induce minor deformations of the parts under load: this benefits both the structural strength of the half-die or of the press that uses it, and the mechanical precision of the forming operation.